This invention pertains to a differential fluid pressure switch used for comparing two fluid pressure inputs and thereby opening a switch contact if a threshold fluid pressure level is exceeded. Such differential fluid pressure switches are typically used on transportation vehicles having front and rear truck units, each of which is equipped with a fluid pressure operated braking system. Fluid pressure comparing devices for such applications typically have designated one input as the high level input and the other input as the low level input. Such a rigid construction does not allow for detection of a condition where the fluid pressure levels are opposite to the preset arrangement. Another feature previously found in a typical differential fluid pressure switch is the use of a preloaded spring or springs for causing the switch contacts to change position. Additionally, another spring would be used to bias the fluid pressure sensitive element which was set to move in response to a predetermined fluid pressure differential. This reliance on a plurality of springs with the inherent spring characteristics, results in high installation and maintenance costs, as shown, for example, by the need to match spring constants of opposing springs, and the need to replace springs whose spring constants have changed due to time and wear. To date, differential fluid pressure switches have also required multiple seal and diaphragm arrangements to be effective. Such an arrangement contributes further to the high maintenance costs which have been typical for such differential fluid pressure switches.